The present invention relates to a method of manufacturing a circuit board to which, for example, an LSI (large scale integrated circuit) is connected.
In known ICs (integrated circuits), a bump acting as a projecting electrode is formed on one surface of an IC element and a conductor of the circuit board is electrically connected to the bump by heating, ultrasonic processing, etc. The conductor and a substrate made of synthetic resin are piled on each other. An opening is formed at a position of the substrate, where the IC element and the conductor coincide in position with each other such that the bump of the IC element and the conductor of the circuit board are placed on each other. Then, heating, ultrasonic processing, etc. are performed so as to electrically connect the conductor and the bump.
FIGS. 1(a) to 1(e) show a known method of manufacturing a circuit board. As shown in FIG. 1(a), perforating is initially performed on a resinous film 1 acting as a substrate so as to form an opening 4. Thereafter, as shown in FIG. 1(b), an electrically conductive metal foil 2 acting as a conductor is bonded to one surface of the resinous film 1. Then, as shown in FIG. 1(c), a protective film 3 is stuck on the other surface of the resinous film 1. Subsequently, as shown in FIG. 1(d), etching is performed on the metal foil 2 such that a necessary circuit pattern is formed on the resinous film 1. Finally, as shown in FIG. 1(e), by peeling the protective film 3 from the resinous film 1, the circuit board is completed.
However, this known method has such a drawback that perforating of the resinous film 1 by press working and sticking and peeling of the protective film 3 are time-consuming operations. Furthermore, the known method has such a disadvantage that a lead-in wire 10 (FIG. 1(e)) for connection to an LSI chip is readily deformed.
FIGS. 2(a) to 2(f) show another prior art method of manufacturing a circuit board. As shown in FIG. 2(a), copper flush plating is initially performed on one surface of a polyimide film 5 acting as a substrate so as to produce an electrically conductive film 6. Subsequently, as shown in FIG. 2(b), resist 7 is coated on the electrically conductive film 6 and on the other surface of the polyimide film 5 and then, is subjected to imaging by exposure and development. Thereafter, as shown in FIG. 2(c), copper additive plating is performed on the electrically conductive film 6 so as to form a circuit pattern 8 on the electrically conductive film 6. Then, as shown in FIG. 2(d), etching is performed on the polyimide film 5 so as to define an opening 9. Subsequently, as shown in FIG. 2(e), the resist 7 is peeled from the electrically conductive film 6 and the polyimide film 5. Finally, as shown in FIG. 2(f), unnecessary portions of the electrically conductive film 6 are removed from the polyimide film 5 and thus, the circuit board is completed.
Meanwhile, this prior art method has such an inconvenience that plating of the electrically conductive film 6 and the circuit pattern 8 and coating, exposure, development and peeling of the resist 7 are time-consuming operations. Furthermore, this prior art method has also been disadvantageous in that the lead-in wire 10 shown in FIG. 2(f) is likely to be deformed.